Everything makes sense when he follows Dean out to the other car. The other car is newer. More streamlined. Prettier. Definitely faster.

That's why Dean likes Assbutt.

"Oh," he says and sounds somewhat disappointed and a little hurt, but then he rallies himself and rumbles out a growl. He's supposed to take Dean to LA, not this... this harlot.

So he walks over to Dean and scoops him up and starts walking out towards the highway like it's perfectly normal. ...He doesn't remember Dean being this heavy.